1. Field of the Invention
The present invention relates to a printer and, more particularly, to a mark detector for detecting the marks which are formed on a label web used as a recording medium of the printer.
2. Description of the Prior Art
In supermarkets or the like, labels indicating the prices and other aspects of commodities are printed and then adhered to the commodities by means of a portable type label printing and applying machine which is called the "hand labeler". When the labels are to be printed with bar codes, that are used in the POS system which has become popular in recent years, the bar codes are required to have high printing accuracy. For such bar code printing, the hand labeler is often not used. Instead, the printing is frequently done by a table type printer.
The labels are supplied in the form of web comprising a number of labels temporarily adhered in series to a web-shaped strip of backing paper. In order to control the label printing and the feed of the label web within the printer, its operation is controlled by forming the label web in advance with marks at predetermined intervals and by detecting those marks by means of an optical sensor.
The label web so marked is guided to pass through the detecting portion of the optical sensor by guide rollers, for example. Just below the sensor of that detecting portion, however, the label web may float or meander while it is running, so that the marks cannot be correctly detected. This may often result in troubles in the operation of the printer.